1. Field of the Invention
This invention relates to a method of manufacturing a magnetic recording medium. In particular, this invention relates to a method of manufacturing a magnetic recording medium used in a hard disk drive and similar. This invention further relates to a magnetic recording medium manufactured using this method of manufacture.
2. Description of the Related Art
As the present state of magnetic information writing onto a magnetic recording medium, after a magnetic recording medium on which no magnetic information is written is incorporated into a hard disk drive (HDD) device, necessary magnetic information is written onto the magnetic recording medium in the HDD in concentric-shape regions having a constant width, called tracks.
Further, data reading and writing is performed while the magnetic head moves along a track on the magnetic recording medium. At this time, the magnetic head detects positional shifts from the track through magnetic signals, called servo signals, written in the magnetic recording medium, and is controlled so as not to deviate from the track.
In order to write servo signals precisely in concentric shapes on a magnetic recording medium on which nothing is written, there is a method of inserting a device having a precise position control function into each HDD from the outside. However, in this method several hours are required to write magnetic information onto tracks numbering several hundred thousand. And, increases in recording density have been accompanied by the need for higher-precision position control devices and for longer write times. Hence the method of inserting a position control device from the outside for each HDD has major disadvantages with respect to productivity and cost.
On the other hand, a magnetic transfer technology and device have been developed by which a transfer master disc having a servo signal pattern is placed in close contact with a magnetic recording medium, and by applying a magnetic field from the outside, the servo signal pattern is instantaneously transferred to the magnetic recording medium.
However, if anomalous protrusions exist in the surface of the magnetic recording medium, when the transfer master disc and the magnetic recording medium are brought into close contact, there may be cases in which the protrusions are collapsed and new protrusions appear in the vicinity thereof, and moreover the protrusions are crushed so that numerous minute protrusions remain over a wide range. If these protrusions exist in the surface of the magnetic recording medium, the protrusions may come into contact with a magnetic head in the HDD, exerting an adverse effect on the head flight.
Hence as for example described in Japanese Patent Publication No. 3587464, after magnetic transfer the magnetic recording medium is subjected to burnishing treatment, and protrusions are cut away and removed.
In recent years, HDD recording capacities have continued to increase, and recording densities of magnetic recording media have also further increased. In order to record on media with such high recording densities, the flying heights of magnetic heads have been steadily lowered, and there have been mounting demands for a smaller distance between the magnetic head and the recording layer of the magnetic recording medium (hereafter also called the magnetic spacing). FIG. 1A shows an example of a conventional magnetic recording medium, i.e., disc-shaped magnetic recording media 100. FIG. 1B, which is a cross-section along A-A′ in FIG. 1A, shows that this structure is generally a layering in succession on a substrate 102 of a magnetic layer 104, a protective layer 106, and a lubricating layer 108.
Hence as means of reducing the magnetic spacing, reduction of the surface roughness of the magnetic recording medium 100, and reduction of the thicknesses of the protective layer 106 and lubricating layer 108 formed on the magnetic layer 104, are conceivable.
In a magnetic recording medium in which the magnetic spacing is reduced in this way, if in the surface there exist minute protrusions and scratches, which previously had not posed problems, then such problems as reduced flying stability of the magnetic head and lowered product manufacturing yields occur, and so a still higher level of flatness is demanded for the surfaces of magnetic recording media.
In light of such circumstances, when employing a method such as that described in Japanese Patent Publication No. 3587464 in which, after magnetic transfer, a magnetic recording medium is subjected to burnishing, and protrusions existing on the medium surface are cut away and removed, the following problem may occur.
When applying a burnishing head for burnishing, there exists certain possibility of contact between the burnishing head and the magnetic recording medium. If the contact occurs, scratches may occur in the medium surface. Thus, the flying stability of a magnetic head may be reduced.
Further, when using burnishing tape in which aluminum oxide abrasive particles are bound to a base film for burnishing, abrasive particles on the burnishing tape may become separated, and the separated particles may be dragged during treatment to cause scratches on the surface of the magnetic recording medium. Thus, the flying stability of a magnetic head may be reduced.
In addition to burnishing after magnetic transfer, there exists another possible cause of reduced flying stability of a magnetic head. When a transfer master disc and magnetic recording medium are brought into close contact in a process of magnetic transfer, mutual transfer to the opposing surface of a lubricating layer between the master disc and the medium. This lubricating layer transfer may cause unevenness in the lubricating layer surface of the magnetic recording medium after magnetic transfer (micro-unevenness of the lubricating layer surface), which may have adverse effects on the flying stability of a magnetic head.
The burnishing performed after magnetic transfer not only adversely affects the flying characteristics of the magnetic head, but may also adversely affect the burnishing head flight and the manner of application of burnishing tape. That is, in the latest magnetic recording media with high recording densities, the surface roughness is small compared with previous magnetic recording media, and so the friction force on the protective layer is high in portions where the lubricating layer is lacking, and the protective layer itself is also thinner, so that unevenness in the surface of the lubricating layer occurring at the time of magnetic transfer can be a cause of more readily occurring scratches in the magnetic recording medium surface during burnishing performed after magnetic transfer.